Some Inter-Continental Ballistic Missiles (ICBM) are equipped with contact fuzes which trigger the detonation of the warhead upon impact against a target or the ground near the target.
In a typical design configuration the vehicle is conical and its front end, referred to as "the plunger", is a solid cone. The plunger is attached at its rear end to the shell constituting the vehicle structure. A contact sensor is normally attached to the rear of the plunger.
Upon terminal impact of the missile, the front end of the plunger generates waves involving strain, stress, and particle velocity. These waves propagate to the back end of the plunger and impose a negative accleration on the sensor causing it to trigger the detonation of the warhead.
Upon terminal impact of the missile the inertia of the sensor mass causes it to move against its spring mount bias, relative to other portions of the sensor. This relative motion, or mass displacement, is used to either open or close an electric circuit for detonating the missile warhead.
The sensor of the present invention is utilized in the circuit closing mode. The mass suspended to a spring undergoes a displacement due to the impact. This closes a "gap" and with that it closes an electric circuit. Upon impact, due to the strain waves propagating backwards along the plunger, the back end of the plunger undergoes a deceleration with respect to the flight velocity V. Due to inertia the mass has a tendency to continue in the same direction with the velocity V. Therefore it undergoes a downward displacement with respect to the casing thus closing the gap and with it an electric circuit.
Premature functioning of contact fuzes during the flight of the missile has been observed and it is attributed to vibrations of aerodynamical origin, such as for instance sudden variations of the shock wave configuration or impact by rain at low altitude so that the fuzing system is already armed. Thus the object of the present invention is to provide a contact fuzing sensor capable of discriminating between vibrations in flight and terminal impact against the target.
It is assumed that the forces imposed on the front end of the missile by aerodynamic perturbations in flight or impact by rain or snow are appreciably smaller than the force imposed by terminal impact. This assumption is valid becuase terminal impact destroys the plunger. If that occured in flight, the missile would be out of service anyway.
It is also known that while the plunger is progressively destroyed by the terminal impact, the deceleration imposed on the backend of the plunger is steadily increasing.
On the contrary, each perturbation in flight may impose a sudden sharp deceleration on the sensor. However, this deceleration will not increase. It may rise as a step but it will subsequently decrease and be damped out.
While each deceleration imposed by perturbations in flight is smaller than the terminal deceleration, a sequence of perturbations imposed on the undamped system may cause the mass to oscillate with an amplitude large enough to close the gap and to trigger the detonation.
The present invention includes a controlled damped massspring system which is the moving part of the sensor. The aim of damping is either to strongly reduce the amplitude of subsequent oscillation or to make the motion aperiodic, so that for each perturbation there will be no subsequent oscillations after the first displacement.
By this means the additive effect of subsequent perturbations in flight is avoided. Then a perturbation in flight is imposed on the plunger, the motion of the sensor's mass due to the previous oscillations is largely reduced by damping. As a consequence, the displacement of the mass is due essentially to the latest perturbation only and therefore it is much less than the deflection under terminal impact.